U.S. Pat. No. 6,984,920 82 describes a piezoelectric motor using longitudinal mode coupling. Here, two groups of piezoelectric plates are placed in between two specifically designed elastic elements with one of them constituting a shaking beam element and with the other constituting a back support element. When both groups of piezoelectric elements are excited with two sinusoidal signals with a specified phase difference, the generated vibration is amplified by the shaking beam element and transferred to a sliding element through frictional contact. However, very precise machining and close manufacturing tolerances of the shaking beam element make it difficult to manufacture the motor at a low cost. Additionally, the vibrating portion of the motor does not have a specific nodal position to hold during operation. Also, one cannot make this motor in a slim form, since the elastic shaking beam element should have a certain length to excite a quarter wavelength of the specific frequency.